1. Field of the Invention
The present invention relates to brushless motors such as a spindle motor, a capstan motor, and a reel motor for driving with a greater torque in high speed and, more particularly, to a brushless motor for use in a compact disk player or CD-ROM drive and a video cassette recorder (VCR) used in the fields of office automation and audio-visual system.
2. Description of the Prior Art
Recently, brushless motors such as spindle motors rotatable at much more faster speeds and with increased torque are required as the development of CD-ROMs which can drive in double-speed and quad-speed of the standard type. To satisfy such requirements, it is also required to develop the brushless motors improved in the perpendicularity of spindle and the discarding the heat generated thereby.
With reference to FIGS. 7 and 8, a conventional spindle motor, as one example of brushless motors, is described below. In FIG. 7, a cross-sectional view of a conventional spindle motor is shown. This conventional spindle motor Mp has a rotor frame 41 including a multi-polarized rotor magnet 42 and a spindle 43. A stator core 44 is comprised of a plurality of core plates each insulated by an insulating material, and is configured to have plural poles corresponding to the multi-polarized magnet 42. Thus formed stator core 44 is further covered by a molded insulator 414 made by molding an insulating material such as resin therearound.
Each pole portion of thus formed stator core 44 is wound up to a wire coil 45 whose ends are soldered to a stator substrate 411 wherein electric circuit components are mounted. The stator core 44 is fixedly supported by a bearing housing 47. The bearing housing 47 also supports a spindle bearing 48. The spindle bearing 48 rotatably supports the spindle 43.
The bearing housing 47 is provided with a first thinner circular wall 420 extending along the axis from the bottom end thereof, and is further provided with a second thinner circular wall 422 around the first circular wall 420. The bearing housing 47 is placed in an opening hole of the stator substrate 411 such that the second circular wall 422 being engaged with that opening hole. The bottom end surface around the second circular wall 422 seats on the upper surface of the substrate 411. A thrust plate 49 is provided at the inner bottom of the bearing housing 47, as inserted inside the first circular wall 420, for receiving the spindle 43 at a thrust receptor 410 formed therein against its thrust force.
Thus prepared bearing housing 47 is installed to the stator substrate 411 by bending up the second circular wall 422 outwardly to caulk it together with the bottom surface of the substrate 47. The first circular wall 420 is bend inwardly to caulk it with the thrust plate 49. Thus, the brushless motor Mp is assembled.
With this type of brushless motor, the upper surface of the substrate 411 which is used as a reference or standard plane for the installation of the bearing housing 47, as described above, is provided with a copper foil 416.
However, the copper foil 416 is adhered to this reference/standard surface of the stator substrate 411 by a non-rigid adhesive agent. Therefore, the surface of thus adhered foil 416 is uneven due to the non-rigidity of the agent even if such adhesive agent can be applied with a uniform thickness. Therefore, the perpendicularity of the bearing housing 47 with respect to the substrate 411 can not be secured.
Since the bearing housing 47 rotatably supports the spindle 43 via the spindle bearing 48, the perpendicularity of the spindle 43 with respect to this reference surface also varies accordingly. This is inevitable even if each of components such as bearing housing 47 and substrate 411 are machined with a high accuracy. As a result, it is very difficult to securely install all the rotation relating members such as spindle 43, bearing 48, bearing housing 47, stator core 44, magnet 42, and rotor frame 41 within a predetermined concentricity.
Furthermore, the dimensional accuracy such as thickness and diameter of the second circular wall 422 after caulking can not be secured. Therefore, the bottom portion of the substrate 411, including the bearing housing 48, can not be used as reference or standard surfaces in both the horizontal and vertical directions for positioning.
As a result, the dimensional accuracy of the spindle motor Mp such as perpendicularity and concentricity of the component members thereof can not be secured when the motor Mp is installed to other mating instruments such as CD-ROM drive and VCR. In this case, therefore, special tools or instruments for detecting and correcting the positions of the rotating members, especially the spindle 43, are necessary to install thus assembled spindle motor Mp accurately. This is inevitable, even if CD-ROM drive's installation place for mating with the brushless motor is machined with a great accuracy.
It is to be noted that it is very difficult to disassemble the conventional brushless motor Mp if once assembled, because the bearing housing 47, thrust plate 49, and the substrate 411 are caulked by the circular walls 420 and 422 with the substrate 411 and the thrust plate 49. Re-caulking the caulked walls 420 and 422 requires great efforts, and causes a unrecoverable damage thereof with respect to the mechanical strength and dimensional accuracy.
Furthermore, the heat generated by wire coil 45 is well insulated by the molded insulator 414 from dissipating to the externals through the heat conductive members of stator core 44, bearing housing 47, bearing 48, spindle 43, and thrust plate 49, and then causes the over heat of the motor Mp. Therefore, a special cooling device is necessary when this type of spindle motor is driven in a higher speed with a greater torque.